A can for packaging products such as food or beverage products comprises a can body to which a can end is fixed by a process known as double seaming. This process requires first forming of a hook on the edge of the open end of the can body (the “body hook”). The curled edge of the can end is then tucked under the body hook and the two are rolled together. This forms the so-called “first operation” seam. The seaming is then completed in a “second seaming operation” in which the hooked seam formed in the first operation is ironed tight for sealing the can end and body together.
Double seam tightness monitors are known from U.S. Pat. No. 4,600,347, for example, in which part of the second operation track of a cam of a double seaming apparatus is deformable. Strain gauges monitor the deformation of this part of the cam track and the signal from the gauges is processed to identify abnormal conditions together with details of the specific force, relevant machine and date/time of each abnormal condition.
Although U.S. Pat. No. 4,600,347 provides details of the force applied during seaming so as to determine the tightness of the seam, this is limited to the second operation cycle of the seaming process in which the seam is tightened for the final seal.
This invention seeks to provide a comprehensive double seam monitor which monitors the whole seaming process from formation of the can body hook through forming of the double seam geometry by the first operation roll, to tightening of the double seam during the second operation.